PubMed Health⌕ Search

Biomedical subjects

T Hogg

Publications and source records attributed to T Hogg.

16 recordsLinked to original sources
PubMed2006

Cellular death of two non-Saccharomyces wine-related yeasts during mixed fermentations with Saccharomyces cerevisiae.

The early death of two non-Saccharomyces wine strains (H. guilliermondii and H. uvarum) during mixed fermentations with S. cerevisiae was studied under enological growth conditions. Several microvinifications were performed in synthetic grape juice, either with single non-Saccharomyces or with mixed S. cerevisiae/non-Saccharomyces inocula. In all mixed cultures, non-Saccharomyces yeasts grew together with S. cerevisiae during the first 1-3 days (depending on the initial inoculum concentration) and then, suddenly, non-Saccharomyces cells began to die off, regardless of the ethanol concentrations present. Conversely, in both non-Saccharomyces single cultures the number of viable cells remained high (ranging 10(7)-10(8) CFU ml(-1)) even when cultures reached significant ethanol concentrations (up to 60-70 g l(-1)). Thus, at least for these yeast strains, it seems that ethanol is not the main death-inducing factor. Furthermore, mixed cultures performed with different S. cerevisiae/ H. guilliermondii inoculum ratios (3:1; 1:2; 1:10; 1:100) revealed that H. guilliermondii death increases for higher inoculum ratios. In order to investigate if the nature of the yeast-yeast interaction was related or not with a cell-cell contact-mediated mechanism, cell-free supernatants obtained from 3 and 6 day-old mixed cultures were inoculated with H. guilliermondii pure cultures. Under these conditions, cells still died and much higher death rates were found for the 6 days than for the 3 day-old supernatants. This strongly indicates that one or more toxic compounds produced by S. cerevisiae triggers the early death of the H. guilliermondii cells in mixed cultures with S. cerevisiae. Finally, although it has not been yet possible to identify the nature of the toxic compounds involved in this phenomenon we must emphasise that the S. cerevisiae strain used in the present work is killer sensitive with respect to the classical killer toxins, K1, K2 and K28, whereas the H. guilliermondii and H. uvarum strains are killer neutral.

Cell Communication↗
PubMed2005

A simple cultural method for the presumptive detection of the yeasts Brettanomyces/Dekkera in wines.

AIMS: The development of a simple and reliable procedure, compatible with routine use in wineries, for the presumptive detection of Brettanomyces/Dekkera from wine and wine-environment samples. METHODS AND RESULTS: The method of detection of these yeasts employs a selective enrichment medium. The medium contains glucose (10 g l(-1)) as carbon and energy source, cycloheximide (20 mg l(-1)) to prevent growth of Saccharomyces, chloramphenicol (200 mg l(-1)) to prevent growth of bacteria and p-coumaric acid (20 mg l(-1)) as the precursor for the production of 4-ethyl-phenol. After the inoculation with wine, the medium is monitored by visual inspection of turbidity and by periodic olfactive analysis. Contaminated wines will develop visible turbidity in the medium and will produce the 4-ethyl-phenol off-odour, which can be easily detected by smelling. CONCLUSIONS: A selective enrichment liquid medium was developed to differentially promote the growth and activity of Brettanomyces/Dekkera. The method is simple to execute, employing a simple-to-prepare medium and a periodic olfactive detection. SIGNIFICANCE AND IMPACT OF THE STUDY: The characteristics of the procedure make it particularly applicable in a wine-making environment thus presenting important advantages to the wine industry.

Culture Media↗
PubMed2003

Carotenoid compounds in grapes and their relationship to plant water status.

The aim of this work was to study the relationship between carotenoid contents in grapevine berries and plant water status. For this purpose, a black grapevine variety, Vitis vinifera L. cv. Touriga Nacional, was studied. The experiments were carried out in the same Douro vineyards, with plants of the same age, in two different water retention soils. A higher water retention capacity soil, soil A, and a lower water retention capacity soil, soil B, were both in a 1.2 m deep silt-loam schist-derived soil. The training system was the double cordon trained and spur pruned. A first range was nonirrigated (NI) and a second one was irrigated (I), 60% of evapotranspiration (ET(0)). For soil B, a 30% of ET(0) treatment was also applied. The plant water status was estimated by predawn leaf water potential. The effects of plant water status on berry growth were studied by measurement of the berry weight and total soluble solids (degrees Brix). The carotenoid profile was quantitatively determined by high-performance liquid chromatography/diode array. Carotenoids determined were beta-carotene, lutein, neoxanthin, violaxanthin, and luteoxanthin. The comparison between irrigated and nonirrigated grapes was followed from 2 weeks before veraison until the ripe stage. Results showed that at harvest time, berries exposed to the NI had a lower weight than those exposed to the irrigated treatment (60% of ET(0)), 0.89 vs 1.36 g/berry and 0.94 vs 1.34 g/berry, for soils A and B, respectively. The irrigated treatment contributed to a higher sugar concentration in both soils. However, depending on the soil water retention capacity, the carotenoid contents were different in soils A and B. For soil A, the total carotenoid content was similar for both NI and I treatments. However, with regard to soil B, in irrigated treatment, levels of carotenoids were approximately 60% lower than those found for the NI. It seems to be possible to produce higher weight berries (with higher sugar levels) with similar carotenoid contents. On the other hand, soil characteristics had a larger influence than irrigation on the concentration of carotenoids in grapes, resulting in an important viticultural parameter to take into account in aroma precursor formation.

Agriculture↗
PubMed2003

Relationship between potentiometric measurements, sensorial analysis, and some substances responsible for aroma degradation of white wines.

Oxidative degradation of white wines can be described sensorially as developing from a loss at positive aroma characteristics, through the development of negative aromas to a linel stage of chromatic alterations. This work attempts to relate the oxidation "status" evaluate by potentiometric titrations, with sensorial degradation and the levels of substances responsible for "off-flavors", such as methional and phenylacetaldehyde. The potentiometric titration employed measures the most powerful antioxidants of white wines (e.g., those which more rapidly consume oxygen). Considering that aromatic precedes chromatic degradation, resistance to oxidation (ROX) constitutes a useful indicator of resistance to oxidation. Sensorial degradation (ID), potentiometric measures, and volatiles were determined both in samples submitted to a "forced aging" protocol and normal aged white wines. High correlation values were observed between ROX and the ID, in both sets (r > 0.87). ID is better explained by ROX values than by the indicated wine age or by the "degree of browning" (Abs = 420 nm). It was also observed that in samples with ROX values higher than 10, the concentration of methional and phenylacetaldehyde were above their respective odor threshold. Finally, it was observed that there is a relationship between oxygen consumption and the respective ROX. Although these results seem very promising, they needed to be further complemented in order to estimate the shelf life of a white wine using potentiometric titrations.

Antioxidants↗
PubMed2002

Citrulline as the main precursor of ethyl carbamate in model fortified wines inoculated with Lactobacillus hilgardii: a marker of the levels in a spoiled fortified wine.

AIMS: The aim of this study was to investigate the production of ethyl carbamate (EC) precursors by Lactobacillus hilgardii in model and Douro fortified wines and to determine the relationship between these compounds and EC levels in this type of wine. METHODS AND RESULTS: Several model fortified wines and fortified wine inoculated with L. hilgardii were analysed for citrulline and EC formation. A good correlation (R > 0.9) was obtained between citrulline and potential EC (that EC which is formed during heating of sample at 80 degrees C for 48 h). CONCLUSIONS: This correlation allowed us to calculate the potential EC formed during lactic acid bacteria activity in fortified wine. SIGNIFICANCE AND IMPACT OF THE STUDY: A good correlation was obtained (R=0.92) between measured and calculated EC in spoiled fortified wines, citrulline apparently being the main EC precursor produced by Lact. hilgardii thus contributing to the potential EC in this type of wine.

Citrulline↗
PubMed2002

Inhibitory mechanisms of antibiotics targeting elongation factor Tu.

Since the pioneering discovery of the inhibitory effects of kirromycin on bacterial elongation factor Tu (EF-Tu) more than 25 years ago [1], a great wealth of biological data has accumulated concerning protein biosynthesis inhibitors specific for EF-Tu. With the subsequent discovery of over two dozen naturally occurring EF-Tu inhibitors belonging to four different subclasses, EF-Tu has blossomed into an appealing antimicrobial target for rational drug discovery efforts. Very recently, independent crystal structure determinations of EF-Tu in complex with two potent antibiotics, aurodox and GE2270A, have provided structural explanations for the mode of action of these two compounds, and have set the foundation for the design of inhibitors with higher bioavailability, broader spectra, and greater efficacy.

Aminoglycosides↗
PubMed2001

Portfolios of quantum algorithms.

Quantum computation holds promise for the solution of many intractable problems. However, since many quantum algorithms are stochastic in nature they can find the solution of hard problems only probabilistically. Thus the efficiency of the algorithms has to be characterized by both the expected time to completion and the associated variance. In order to minimize both the running time and its uncertainty, we show that portfolios of quantum algorithms analogous to those of finance can outperform single algorithms when applied to the NP-complete problems such as 3-satisfiability.

Journal Article↗
PubMed2001

A new lysozyme fold. Crystal structure of the muramidase from Streptomyces coelicolor at 1.65 A resolution.

Cellosyl is a bacterial muramidase from Streptomyces coelicolor. Similar to other lysozymes, the enzyme cleaves the beta-1,4-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine units, but it also exhibits a beta-1,4-N,6-O-diacetylmuramidase activity. The latter enables Cellosyl to degrade the cell walls of Staphylococcus aureus, which are not hydrolyzed by chicken-, goose-, or bacteriophage T4-type lysozymes. The enzymatic activity and amino acid sequence of Cellosyl group it with lysozymes of the Chalaropsis type, for which no detailed structural information has been available so far. The crystal structure of Cellosyl from S. coelicolor has been determined to a resolution of 1.65 A and refined to an R-factor of 15.2%. The enzyme is comprised of a single domain and possesses an unusual beta/alpha-barrel fold. The last strand, beta 8, of the (beta/alpha)(5)beta(3)-barrel is found to be antiparallel to strands beta 7 and beta 1. Asp-9, Asp-98, and Glu-100 are located at the active site. The structure of Cellosyl exhibits a new lysozyme fold and represents a new class of polysaccharide-hydrolyzing beta/alpha-barrels.

Amino Acid Sequence↗
PubMed1997

An Economics Approach to Hard Computational Problems

A general method for combining existing algorithms into new programs that are unequivocally preferable to any of the component algorithms is presented. This method, based on notions of risk in economics, offers a computational portfolio design procedure that can be used for a wide range of problems. Tested by solving a canonical NP-complete problem, the method can be used for problems ranging from the combinatorics of DNA sequencing to the completion of tasks in environments with resource contention, such as the World Wide Web.

Journal Article↗
PubMed1989

The stability of ecosystems.

Stability criteria and phase boundaries for complex ecosystems are obtained and contrasted with previously studied scenarios. The stability of such systems is determined by the behaviour of the largest eigenvalue of matrices governing the response of the system to small perturbations. As a result we show that ecosystems with unstructured cooperative interactions between arbitary species can be less stable than had been previously determined. We also examine hierarchical ecologies, and demonstrate their increased stability under certain conditions.

Animals↗
PubMed1988

A graph-dynamic model of the power law of practice and the problem-solving fan-effect.

Numerous human learning phenomena have been observed and captured by individual laws, but no unified theory of learning has succeeded in accounting for these observations. A theory and model are proposed that account for two of these phenomena: the power law of practice and the problem-solving fan-effect. The power law of practice states that the speed of performance of a task will improve as a power of the number of times that the task is performed. The power law resulting from two sorts of problem-solving changes, addition of operators to the problem-space graph and alterations in the decision procedure used to decide which operator to apply at a particular state, is empirically demonstrated. The model provides an analytic account for both of these sources of the power law. The model also predicts a problem-solving fan-effect, slowdown during practice caused by an increase in the difficulty of making useful decisions between possible paths, which is also found empirically.

Decision Making↗
PubMed1984

Understanding biological computation: reliable learning and recognition.

We experimentally examine the consequences of the hypothesis that the brain operates reliably, even though individual components may intermittently fail, by computing with dynamical attractors. Specifically, such a mechanism exploits dynamic collective behavior of a system with attractive fixed points in its phase space. In contrast to the usual methods of reliable computation involving a large number of redundant elements, this technique of self-repair only requires collective computation with a few units, and it is amenable to quantitative investigation. Experiments on parallel computing arrays show that this mechanism leads naturally to rapid self-repair, adaptation to the environment, recognition and discrimination of fuzzy inputs, and conditional learning, properties that are commonly associated with biological computation.

Adaptation, Physiological↗
PubMedDate not supplied

The importance of good record-keeping.

When large numbers of health care staff from different professional groups are involved in the care of individual clients, the need for simple, understandable, uniform casenotes becomes paramount. This article describes how a survey of the different casenotes used by various CPN teams led to the devising of a new system. The aim was to encourage good practice and develop a standardised record-keeping system.

Community Health Nursing↗